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Accounting for Organic Compound Volatility in Standard Emissions Speciation Profiles, Databases and Models
Citation:
Pouliot, G., B. Murphy, H. Pye, M. Qin, Q. Lu, AND A. Robinson. Accounting for Organic Compound Volatility in Standard Emissions Speciation Profiles, Databases and Models. 2019 International Emissions Inventory Conference, Dallas, TX, July 29 - August 02, 2019.
Impact/Purpose:
Profiles for mobile sources (vehicles, offroad mobile, and aircraft) that explicitly distribute organic mass among low volatility, semivolatile, intermediate volatility and volatile organic compounds (LVOCs, SVOCs, IVOCs, and VOCs, respectively) offer a more complete picture of emissions in these ranges, and the resulting SOA formation that follows. Much of the uncertainty surrounding potentially underrepresented mass in the SVOC and IVOC ranges can be reduced if relevant experimental information (e.g. particle concentration, temperature, organic aerosol concentration, etc) is reported with published profiles
Description:
It has been shown that primary organic aerosol (POA) mass from combustion emissions evaporates as it is diluted to ambient conditions. Large-scale model studies have also shown that treating POA compounds as semi-volatile and accounting for secondary organic aerosol (SOA) from underreported precursor emissions has a significant impact on the average contributions from combustion sources as well as on the spatiotemporal variability of OA concentrations, particularly in urban areas and downwind of sources. Although many chemical transport models (CTMs) now include POA semi-volatile partitioning, standard emission databases (e.g. SPECIATE) and methods have only begun to account for these phenomena in emission profiles. With the release of SPECIATEv5.0, we have introduced profiles for mobile sources (vehicles, offroad mobile, and aircraft) that explicitly distribute organic mass among low volatility, semivolatile, intermediate volatility and volatile organic compounds (LVOCs, SVOCs, IVOCs, and VOCs, respectively). The profiles have been shown to be highly consistent with existing mobile profiles in the VOC range. But much of the IVOC and SVOC mass has been underrepresented in the past and the new profiles offer a more complete picture of emissions in these ranges, and the resulting SOA formation that follows. To accommodate these important classes of pollutants, we have added new species to the SPECIATE database, with properties chosen to effectively propagate information about the partitioning behavior of emissions from individual sources to downstream models, including large-scale 3D models. This presentation will discuss the details of the new profiles and species with specific focus on similarities to and differences from existing profiles. We have also found that much of the uncertainty surrounding potentially underrepresented mass in the SVOC and IVOC ranges can be reduced if relevant experimental information (e.g. particle concentration, temperature, organic aerosol concentration, etc) is reported with published profiles. SPECIATEv5.0 will accommodate this information where available. Finally, we will discuss how inventory models might evolve to better incorporate emerging information made available by more complex measurement techniques, and how these models might support more sophisticated air quality investigations.